Heat shrink lay-flat width to diameter calculator
Convert the edge-to-edge width of unheated, flattened heat shrink tubing to its approximate round diameter, or calculate the flat width from a round diameter. A 40 mm flat width corresponds to about 25.46 mm round diameter in the thin-wall approximation.
Formula and reference table
A flattened tube has two faces. Their combined width approximates the circumference of the same tube when opened into a circle. Measure the supplied tubing and check its expanded and recovered sizes when fitting it to a component.
- Round diameter ≈ 2 × lay-flat width ÷ π
- Lay-flat width ≈ π × round diameter ÷ 2
| Lay-flat width (mm) | Approximate round diameter (mm) |
|---|---|
| 10 | 6.37 |
| 20 | 12.73 |
| 40 | 25.46 |
| 60 | 38.20 |
| 80 | 50.93 |
| 100 | 63.66 |
Which dimension should I give the cutter supplier?
Measure flat stock across both outer edges while it lies relaxed, without pulling it. For round stock, send the actual outside diameter and wall thickness. Include the cut length and whether the material arrives flat on a reel or open and round. Thick or adhesive-lined tubing can depart from the thin-wall estimate, so use the drawing or measure a sample when fit is tight.
The automatic heat shrink and PVC tube cutter WM-608 lists a 0–100 mm cutting width across the blade path. Send the measured width for flat stock, or the actual outside diameter and wall thickness for round stock, so we can check the feed setup. For sizing over a component, use the tubing maker's expanded and recovered inside diameters. For final sleeve length, see our heat shrink cut-length guide.
For side-by-side feeding, the geometric limit is the usable width plus one gap, divided by the flat width plus one gap, rounded down. Roller grip and guide spacing determine how many lanes run together in practice. Pieces per running hour are measured cuts per minute × verified lanes × 60, before pauses or rejected pieces.
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